Centrifugal clutches



June 6, 1961 Filed Feb. 5, 1958 J. MAURICE ET AL CENTRIFUGAL CLUTCHES 5Sheets-Sheet 1 June 6, 1961 .1. MAURICE E AL CENTRIFUGAL CLUTCHEIS5\Sheets-Sheet 2 Filed Feb. 3, 1958 June 6, 1961 Filed Feb. 3, 1958 J.MAURICE ETAL CENTRIFUGAL CLUTCHES 5 Sheets-Sheet 3 June 6, 1961 J.MAURICE ET AL CENTRIFUGAL CLUTCHES 5 Sheets-Sheet 4 Filed Feb. 5, 1958J. MAURICE ET AL June 6, 1961 CENTRIFUGAL CLUTCHES 5 Sheets-Sheet 5Filed Feb. 3, 1958 United States Patent 0.

' 2,987,155 QENTRIFUGAL CLUTCHES Jean Maurice and Michel Rist, Paris,France, assignors to Societe Anonyme Francaise du Ferodo, Paris, France,a corporation of France Filed Feb. 3, 1958, Ser. No. 712,810 Claimspriority, application France Feb. 4, 1957 3 Claims. (Cl. 192-48) Thepresent invention relates to centrifugal clutches of the type in whichthe weight-head carrier is either driven at will by the driving shaft orkept stationary or braked, especially by a fixed electro-magnet, thearmature of which is fixed for rotation with the weight-head carrier andis intended to make contact through friction linings with a cover orcasing fixed to the driving shaft. The invention relates moreparticularly to such clutches in which the weight-heads co-operate witha cam mounted so as to be fixed for lateral movement and free forrotation on a transfer plate which transfers its thrust to at least onepressure plate through clutch springs, whilst a stop limits thecentrifugal travel of the weight-heads. A centrifugal clutch of thistype is described and shown in our United States Patent No. 2,850,131.

In the known clutches of this type, this stop is generally formed by theweight-head carrier itself, and the latter is in moulded steel and ismachined so as to resist the stresses applied at the point of the stop,whilst having the required durable precision. This results in a highcost of manufacture and a troublesome inertia of the weight-heads. Inaddition, difliculties are encountered in regulating the relativeposition of the electro-magnet and of its armature, whilst the centeringof the armature with respect to the weight-heads and its return towardsthe casing are defective. Undesirable noise is observed when thearmature is attracted to the electro-magnet and/or when it is returnedtowards the casing. In addition, the inertia of the friction assembly ofthe clutch is considerable and interferes with its satisfactoryoperation.

One object of the invention is to simplify the manufacture of theweight-heads and to enable them to be of light construction, a specialfeature being that the stop which limits the centrifugal travel of theweight-heads is formed by an edge of this cam. This edge is preferablycovered with an anti-noise lining and has preferably a safety surfaceadjacent to this lining so as to replace it when it is no longer activeand without causing jamming.

The objects, particular features and advantages of the invention willfurther be made clear from the description which follows below of formsof embodiment chosen by way of example, reference being made to theaccompanying drawings, in which:

' FIG. 1 is a view in longitudinal cross-section of a centrifugal clutchin accordance with the invention.

' FIG. 2 is a view in elevation in the direction of the arrows 11-11 ofFIG. 1, of a portion of the said clutch.

FIG. 3 is a view in elevation, in the direction of the arrows III-III ofFIG. 1 of a further part of the clutch. FIG. 4 is a view similar to thatof FIG. 1, but relates to an alternative form of centrifugal clutch inaccordance with the invention.

FIG. 5 is a view of the de-clutching electro-magnet of FIG. 4 inelevation in the direction of the arrows V-V of FIG. 4, and comprises adiagram of the electric supply of this electro-magnet.

FIGS. 6 and 7 are detail views to a slightly enlarged scale,respectively in cross-section taken along the line VI-VI and the lineVII-VII of FIG. 5.

FIG. 8 is a view of the device of FIG. 7 taken along the broken lineVIII-VIII of FIG. 7.

2,9871% Patented June 6, 1961 ice FIG. 9 is a view of the friction discfollowing the broken line IX-IX of FIG. 4.

FIG. 10 is a view to a large scale of the weight-head of FIG. 4 in itsposition of abutment on the cam.

In the form of embodiment shown in FIGS. 1 to 3, which concerns anapplication (without any implied limitation) of the invention toautomobile vehicles, there can be seen in FIG. 1 at 10 the driving shaftand at 11 the driven shaft of the centrifugal clutch in accordance withthe invention. The gripping plates of the clutch are constituted, one bythe fly-wheel 12 which is fixed to the shaft 10 and which carries thestarter crown-wheel 14,. and the other 13, which is mounted fast forrotation but free for lateral movement with respect to the fly-wheel 12.

The plates 12 and 13 are intended to grip a frictiondisc 15 which ismounted fast for rotation and sliding on the driven shaft 11. The disc15 carries a ratchet-wheel 16 (see FIGS. 1 and 3) the teeth 17 of whichco-operate with pawls 18 carried by the fiy-wheel 12. Each pawl 18 ispivotally mounted on a shaft 19 so as to move away from the teeth 17 ofthe wheel 16 when it is subjected to the action of centrifugal force dueto rotation of the driving shaft. A blade return-spring 20 is providedon each pawl 18 in order to engage it in the teeth 17 when thecentrifugal force is insufficient to move it away, and especially whenthe driving shaft is stopped.

With each tooth 17 of the wheel 16 is associated a mask 21 of bent steelsheet, which has the shape of a saddle and which is pivotally mounted at22 on the wheel 16 so as to be raised above the tooth and to prevent theengagement of the pawl with the tooth when this mask 21 is subjected tothe action of centrifugal force due to the rotation of the driven shaft.A helicoidal return-spring 23 is provided on each mask 21 in order towithdraw it beneath the tooth 17 when the centrifugal force isinsufiicient to lift it, that is to say when the driven shaft is stoppedor rotates slowly, for example at a speed less than 180 rpm. The mask 21is preferably provided with lateral extensions 24 beyond the summit 25of the saddle so as to increase its sensitivity to the action ofcentrifugal force.

It will be noted that the device 21 is light and simple to mount, andthat the helicoidal spring 23 ensures precise operation.

When the engine is running, the pawls 18 are freed from the teeth 17 andare inactive. When the engine is not running, the pawls 18 engage in theteeth 17, which enables the engine to be driven by the vehicle and alsoallows the vehicle to be locked in position during parking, by theeffect of the engine compression. However, when the vehicle is runningat an appreciable speed and a the engine stops unexpectedly, the masks21 prevent the pawls from coming into engagement with the teeth 17.

' A torque-limiting device 26 may be interposed between the wheel 16 andthe shaft 11. It is preferably arranged so as to limit the torquetransmitted in reverse and thus to prevent skidding of the drivingWheels of the vehicle. The limiter device 26 is preferably of the typedescribed later in detail in connection with FIG. 9.

The centrifugal mechanism of the clutch (see FIG. 1) is housed in acover or casing 27 fixed to the fly-wheel 12. This fixation preferablyconsists of screws screwed into the fiy-wheel 12 and clamping the casing27 against an elastic block 81 inset in the fiy-Wheel 12, which isprovided with a safety shoulder 82. This arrangement enables noise to beeliminated or reduced at the moment when the electro-magnet 58 attractsor releases the armature 57, which will be described in detail later.The centrifugal mechanism of the clutch controls the clamping of theplate 13 against the friction-disc 15 which itself has just been grippedby forcing against the plate 12.

3 When the centrifugal mechanism does not act on the plate 13, thelatter frees the disc 15 due to the action of release springs (notshown) which act between the plates 12 and 13. It has been found thatwhen the .de-clutching play of the plate 13 is considerable, shocks andnoise are produced when re-engaging the clutch. In order to remedy thisdefect, the return movement of the plate 13 is made controllable, inaccordance with the invention, by means of stops 28 interposed betweenthe plate 13 and a member fixed to the plate 12, such as the peripheryof the casing 27. The stops 28 are uniformly distributed in circularsymmetry and are for example three in number. Each stop 28 consists of ascrew, the body of which is screwed into a threaded hole in the plate13, and the head 29 of which extends between the plate 13 and the casing27, whilst at the other extremity a lock-nut 30 is screwed oh the screw28. The varying extent to which the screws 29 are screwed into the plate13 enables the limit of the return travel of the plate 13 to beregulated at will. A regulation of this kind can be carried out once andfor all at the time of assembly without there being any subsequent needto modify it in order to take account of wear in the linings of the disc15, the limited travel of the plate 13 remaining usually always fairlysmall so as to ensure silent operation.

It should be noted that the return travel of the plate 13 can be stoppedbefore the stops 28 come into efiective action, by the effect of anelimination of the successive plays between the parts which are locatedbehind the plate 13. These parts comprise a transfer plate 31, a cam 32,weight-heads 33, a weight-head carrier 34, which are described in detaillater, and finally the casing 27.

This will take place when the weight-heads come into contact with thecam, if the sum of these successive plays is small, but the stops 28ensure in any case that the return travel of the plate 13 does notexceed the limit fixed by the setting of the said stops 28, andconsidered as preventing any undesirable shock or noise in the vicinityof the plate 13, even if the said sum of plays were greater than thelimit.

Actually, when this sum of plays is large, which implies the activeintervention of the steps 28, this intervention increases the approachtravel of the weight-heads 33 towards the cam 32. Tests have shown thatthe contact of the weight-heads with the cam takes place without shockand can practically not be felt, doubtless because of the inclination ofthe surface of the cam at the point where the play between the cam andthe weight-heads is eliminated. Y

The transfer-plate 31, which is located immediately behind the plate 13,is slidably mounted on this plate by tenons 35 and mortices 36. Thedistance between the plates 31 and 13 is limited by small plates 37 andscrews 38. The clutch springs 39 are applied against the plate 13through the intermediary of heat-insulating washers 40 intended, whenthe plate 13 becomes hot, to prevent the transmission of its heat to thesprings 39 thus tending to alter their calculated properties. Thesprings 39 are housed in sockets 41 which are supported against thetransfer-plate 31.

The cam 32 is mounted free for rotation on the transfer-plate 31 bymeans of a ball-bearing 42 and co-operates with rollers 43 of theweight-heads 33 which are pivotally mounted at 44 on the weight-headcarrier 34. The rollers 43 are mounted on needle-bearings 45 on theweight-heads 33 and have a continuous rolling surface which is free fromholes. The pivotal shafts 44 of the weight-heads on the weight-headcarrier 34 are also provided with needle-bearings 46. The weight-headcarrier 34 is itself mounted for free rotation on the casing 27 by meansof a ball-bearing 51.

Means provided for protecting the bearings 42 and 51 and theneedle-bearings 45 and 46 against dust consist of a ring 70 of felt orother suitable elastic material, and/or which is an absorbent for thelubricant, fixed to Mme r the casing 27 by a sheet steel ring 71 screwedon to this casing at 72. Against the ring 70 is applied a bell 73 whichis fixed at 74 to the transfer-plate 31 and having flexibility so as tobe able to slide on the ring 70 while retaining therewith a fluid-tightrelation during the course of the axial movements of the plate 31.

In addition, in order to keep the bearings 42 and 51 well lubricated,lubricant casings 77 are provided and are made fluid-tight by joints ofplastic material, at least at the time of assembly, having a base ofrubber or of polymerisable glue or jointing paste. These joints areapplied not only at the points at which the leakage of lubricant isliable to occur as a result of centrifugal force, such as 75, but alsoat points at which this leakage may take place due to a siphon elfectdue to the indirect action of centrifugal force, such as 76.

The oscillation travel of the weight-heads 33 on the weight-head carrier34 is limited towards the axis by an anti-noise washer 47 fixed to theweight-head carrier 34 and intended to receive the rollers 43 inabutment. This travel is limited towards the exterior by an edge 48rigidly fixed to the cam, internally lined by an antinoise washer 49 andintended to receive in abutment the bearing surfaces 50 of theweight-heads.

The provision of a stop for the weight-heads towards the exterior on thecam at 48 and 49, rather than on the weight-head carrier 34, enables thelatter to be freed from large stresses,'so that it no longer needs to bemade of moulded steel but can be of light material or alloy. The inertiaof the weight-head carrier is thus reduced with advantage, which ensuresa more rapid response of the weight-head carrier when it is requiredeither to be run-up to high speed or to be braked. In addition, theweight-head carrier 34 may then be made by casting in its semi-finalform. It does not require to be subjected to costly milling operations,whilst the machining of the weight-heads 33 is itself simplified and isreduced only to the bearing surfaces 50 which are turned in thedisplaced position of the weight-heads.

The weight-head carrier 34 is provided with a hollow central boss 52which extends towards the rear inside the bearing 51 and round the shaft11. A flange 53 which extends behind the casing 27, is positively fixedby screws 54 to the extremity of the boss 52, whilst a number offlexible radial blades 55 (see FIGS. 1 and 2) extend between the flange53 and the casing 27, and are gripped between the members 52 and 53 bythe screws 54. At their outer extremities, the blades 55 are fixed byrivets 56 to a magnetic armature 57 which they thus maintain correctlycentered and rigidly fixed for rotation, whilst by virtue of theirflexibility they permit axial movements of the said armature.

The rear face of the armature 57 co-operates with a fixed immobilisingelectro-magnet 58, the circuit of which is closed during the operationsof gear-changing and is open when these operations are not taking place.In more detail the circuit feeding the coil of the electromagnet 58comprises the battery of the vehicle, the ignition contact 116 and aswitch 117 which is incorporated in the gear-changing lever 118. Theswitch 117 is controlled by the lever 118 so as to be closed during thecourse of gear-changing operations to energize the electromagnet 58 andto be open except during these operations to deenergize the saidelectromagnet. A capacitor 119 and a resistor 120 having a very ;highresistance are provided in parallel with the switch 117 to protect thecontacts without excessive consumption. As shown in FIG. 1 it isunderstood that the circuit is completed by grounding of one terminal ofthe battery 115 and of one terminal of the switch 117. The capacitor 119and the resistor 120 are also grounded as shown. The front face of thearmature 57 is lined with arcuate elements 59 of friction material whichalternate with the blades 55. The elements 59 are intendedto be infrictional engagement with the casing 27 and have a section of steppedor tiered form (see FIGS. 1 and 2) so that only their portion 60 whichis the closest to the axis and to the springs 62 is permitted to comeinto contact, whilst the other portion 61 is not in contact.

The supporting surfaces of the linings 59 on the armature 57 is largesince, in addition to the active portion 60, it comprises the portion61. This permits of a very strong adhesion of the linings 59 on thearmature 57 and results in complete suppression of noise and vibration.In addition, the reduced radial width of the active portion 60 permits asatisfactory application against the casing 27, even if the armature orthe casing are not strictly fiat or become deformed during the course ofoperation. The application pressure is increased, which on the one handprevents any polishing action likely to reduce the coefiicient offriction of certain linings, and on the other hand, it acceleratesrunning-in.

Helicoidal application springs 62 distributed in circular symmetry andarranged in the vicinity of the active parts 60 of the elements 59, actbetween the flange 53 and the armature 57 so as to ensure theapplication of the elements 59 against the casing 27 when theelectromagnet 58 is de-excited, the blades 55 taking no substantial partin this applying action and serving only to keep the armature 57centered during the course of its movements, and to form a coupling fastfor rotation between the armature and the weight-head carrier.

The coefficient of elasticity of the helicoidal springs 62 may be chosento be small since these springs, which are distant from the axis arenumerous, twelve in the example shown, and by their helicoidal naturehave a strength which varies only slightly with variations inelongation, due to wear of the linings 59. For the same reason, it ispossible to dispense with the provision of accurate movable adjustmentwedges. The force of application being distributed very uniformly in theimmediate vicinity of the zone of application 60, a large transmittedtorque is obtained for the same effort. This torque is subject only tonegligible variations during working. The pre-stress of the set ofsprings may be made moderate by reason of the fidelity of thecharacteristics of the springs 62, which enables the restoring force ofthe electromagnet 58 to be limited.

In the alternative form of embodiment shown in FIGS. 4 to 10, thearrangement is'similar to that which has just been described withreference to FIGS. 1 to 3, and the same reference numbers have been usedin FIGS. 4 to and in FIGS. 1 to 3 to indicate similar parts.

In the alternative form of FIGS. 4 to 10, there can be seen at 85 thefixed casing in which the centrifugal clutch is housed. There is againseen at 12 and 13 the gripping plates of the friction-disc 15. As in theprevious case, the disc 15 carries a ratchet-wheel 16, which is in thiscasein the form of a bell of stamped steel sheet, and the ratchet teeth17 of which are small cut-out plates which are fixed in position. Theteeth 17 co-operate with the pawls 18 pivotally mounted at 19 on thefly-wheel 11. With each tooth 17 is associated the mask 21, pivoted at22. The torque-limiter 26 is interposed between the disc 15 and theshaft 11 and comprises (see FIGS. 4 and 9) a wedging member 86 which isfixed to the disc 15 and to the wheel 16, and which co-operates withshoes 87. The latter rub against a drum 88 which is rigidly fixed to thehub 89 of the disc engaged by flutings on the shaft 11, springs 90 beinginterposed between the member 86 and the shoes 87. The member 86 and theshoes 87 are of cast-iron and respectively comprise large hollowedportions 91 and 92, so that the inertia of the assembly of the disc 15with the wheel 16 and the limiter 26 is reduced.

There is again shown at 31 the transfer-plate and at 39 the clutchsprings which are strongly pre-stressed. The pressure plate 13 has asafety bearing surface 93 from which the transfer-plate 31 is separatedat its periphery by a very small radial clearance in order to limit therelative displacements which might occur after prolonged wear. Theheat-insulating washer 40, interposed between the spring 39 and theplate 13 is in this case provided with a stamped undulating shape forthe circulation of air.

There is again shown at 32 the cam which co-operates with the rollers 43of the weight-heads 33, pivoted at 44 on the weight-head carrier 34.Each weight-head 33 is in abutment in its position of rest against thebuffer 47 of flexible material of the weight-head carrier and in themaximum centrifuged position is in abutment against the anti-noisewasher 49 of elastic material which is fixed, preferably by sticking, tothe edge 48 of the cam 32. There is seen more particularly in FIG. 10 at50 the bearing surface of the weight-head 33 which is intended to beapplied against the washer 49. The washer 49 is in this case embedded inthe edge 48, which has an adjacent face 94 slightly below the level ofthe washer 49 when the latter is new. By means of this arrangement, ifthe washer 49 does not function any more for any particular reason, thebearing surface 50 of the weight-head would find in the last resort asupport which remains suitable, against the face 94, the latterconstituting in this way a safety abutment such that any jamming of theweightheads is prevented.

The weight-head carrier 34 (see FIG. 4) is preferably of light alloy andis carried through the intermediary of the bearing 51 by the casing 27which is in this case of stamped steel sheet and has a double edge 95 inorder to receive and house the outer track of the bearing 51.

The face of the armature 57 which is turned towards the casing 27 islined with elements 59 of friction material, which alternate with theblades 55. The linings 59 have preferably a base of cork or are of theusual friction material, and are carried through the medium of anelastic under-layer 96 of cork or rubber in order to prevent noise. Forthe same purpose, a stack of steel sheets could be provided on thecasing at the point where the linings 59 are in rubbing contact.

The opposite face of the armature 57 co-operates with a fixedimmobilising electro-magnet, of which the yoke is shown at 97 and thecoil at 58. The yoke 97 (see FIGS. 4 to 8) is provided in this case withthree outer lugs 99 each comprising a threaded hole 100 parallel to theaxis of the clutch, and a dished portion 101 directed towards the fixedcasing 85. In the dished portion 101 is housed a pastille 102 of hardmaterial.

A screw 103 having a cylindrical neck 104 and a hexagon head 105, passesfreely through a hole 106 in the fixed casing 85 and is screwed intoeach threaded hole 100 in the yoke 97, while a screw 107 having a longhexagon head 108 is screwed into a member 109 rigidly fixed to thecasing 85, and is intended to abut against the pastille 102. A clip 110intended to prevent accidental slackening of the screws is engaged roundthe collar 104 and grips the head 108. Washers 111 are ar ranged roundthe collar 104 between the clip 110 and the casing 85. The two heads and108, the clip and the washers 111 are located on the outer side of thecasing 85.

This arrangement enables the position of the electromagnet 97 to bedefined with convenience and precision with respect to the armature 57both at the time of assembly and after a period of service when thelinings 57 will be worn, in order to maintain the air-gap existingbetween the yoke 97 and the armature 57 at a precise and suitable value.

In order to carry out this adjustment, the three screws 103 are first ofall screwed sufiiciently to bring the yoke 97 into contact with thearmature 57 which gives a faithful and precise reference point. Theneach screw 103 is unscrewed by an amount previously determined, forexample one or a number of turns or fractions of turns, which moves theyoke 97 away from the armature while keeping it parallel to theconjugate face of this armature.

The screw 107 is then screwed-up to the abutment at 102, which locks theyoke 97 in the desired position.

I It will be noted from FIG. 4 that thepole face of the yoke 97 isprovided on each side of the coil .58 with two annular beads of materialwith a base of cork, these heads 121 projecting slightly. Thisarrangement is intended to prevent noise, both by the elastic action ofthe beads 121 and by the dash-pot effect which they produce. In order toavoid any excessive suction of air between the beads, there canpreferably be provided in the beads 121 several narrow passages throughwhich the air is forced wih a throttling effect. It is to be noted thatthe dashpot effect could be produced by projections formed in thearmature 57. In the same way, an elastic action only could be providedand obtained by a single bead 121 with a base of cork, in particular theouter bead, instead of two.

One of the lugs 99 (see FIGS. 5 and 6) is provided with insulatingsupports carrying two electric terminals 112 and 113 which arerespectively coupled to the two ends of the coil 58 by conductors 114passing behind the yoke 97, that is to say without causing anydiscontinuity in the pole faces of either the yoke 97 or in the beads121. The terminal 112 is supplied by the battery 115 of the vehiclethrough the intermediary of the ignition contact 116, while the terminal113 is grounded through the medium of the switch 117. So in FIGURE 1,the switch 117 is controlled by the gear-changing lever 118 so as to beclosed during the course of gear-changing operations and to be openexcept during these operations. The capacitor 119 and the resistor 120may-be also provided in parallel with the switch 117.

What we claim is:

1. In a centrifugal clutch of the kind comprising: a driving shaft and adriven shaft; a friction drive unit, including a fly-wheel fast withsaid driving shaft, a pressure-plate fast for rotation with said drivingshaft but axially movable with respect thereof and a friction disc fastfor rotation with said driven shaft and axially slidable thereon, saidfriction disc being located between said fly wheel and saidpressure-plate and being provided with friction linings for beinggripped between said flywheel and said pressure-plate when the clutch isengaged; a dished casing fixed to said fly-wheel; and a centrifugal unithoused in said casing, said centrifugal unit including a transfer-plateaxially slidable on said pressure-plate and fast for rotation therewith,a plurality of axially-mounted clutch springs between said transferplate and saidpressure plate, an annular cam mounted freely rotatableand fast for axial movement on said transfer-plate, and a weight-headcarrier mounted freely rotatable on said casing and carrying pivotedweight-heads cooperating with said cam, said weight-heads being pivotedon said carrier so that they'are pushed axially against said cam bycentrifugal force, the axial thrust of said weight-heads on said cambeing transferred through said transfer-plate and said clutch springs tosaid pressure-plate, the combination with said cam and weight-heads ofan abutment member extending towards the weight-heads and encirclingthem to be abutted by them, the said abutment being constituted by aperipheral axially-projecting annular member forming part of the saidcam.

2. A clutch as claimed in claim 1, in which the internal face of saidabutment with which the weight-heads make contact is provided with aninset lining ring of rubber like material.

3. A clutch as claimed in claim 2, in which the said ring projects onlyslightly from the inner surface of said annular abutment, the said innersurface acting as a stop for the said weight-heads when the lining ringbecomes worn.

References Cited in the file of this patent UNITED STATES PATENTS1,810,360 Loeffler June 16, 1931 2,107,075 Lyman Feb. 1, 1938 2,278,547Herrington Apr. 7, 1942 2,280,736 Winther Apr. 21, 1942 2,301,600 WilsonNov. 10, 1942 2,400,625 Bloomfield May 21, 1946 2,462,457 Berndtson Feb.22, 1949 2,559,765 Gravina et a1. July 10, 1951 2,635,722 Wemp Apr. 21,1953 2,729,310 Le Tourneau Jan. 3, 1956 2,774,452 Wisman Dec. 18, 1956FOREIGN PATENTS 151,478 Great Britain Sept. 30, 1920 829,954 France May2, 1938 568,409 Great Britain Apr. 4, 1945 1,066,576 France Ian. 20,1954 1,086,389 France Aug. 11, 1954 1,133,704 France Nov. 19, 19561,134,189 France Nov. 26, 1956

